Measurement of Unsteady Airloads on an Oscillating Engine and a Wing-Engine Combination.

Experimental investigations of unsteady aerodynamic forces were performed on an oscillating ejector engine model and a wing/engine combination in the subsonic and transonic flow regimes. The experimental results were compared with theoretical results. The aim was to determine how well, in reality, the mathematical aerodynamic models commonly used for flutter calculations correspond to the flow conditions on an engine. The investigations on the isolated ejector engine demonstrated that linear lifting surface theory provides quite accurate unsteady aerodynamic forces. The effects of the Mach number and reduced frequency are described correctly. For the wing/engine combination, the unsteady interference effect of the engine oscillation on the lower side of the wing is strongly influenced by flow separation at the wing/pylon connection. In general, the unsteady aerodynamic forces induced by the engine on the wing are small and are therefore of minor influence on the unsteady airloads of an oscillating wing